Image Production

Mosbys Exam Practice

Which of the following best describes the shape of the x-ray beam utilized in multidetector CT (MDCT)?

a. pencil beam

b. fan-shaped

c. electron beam

d. cone-shaped

cone shaped

Collimation of the CT x-ray beam occurs:

1. at the x-ray tube, regulating slice thickness

2. just beyond the patient, focusing off-axis transmitted radiation

3. before the detectors, limiting the amount of scatter radiation

absorbed

a. 1 only

b. 1 and 2 only

c. 1 and 3 only

d. 1, 2, and 3

1 and 3 only

CT numbers are usually provided in the form of:

a. hounsfield units
b. EMI numbers
c. cormacks
d. μ

hounsfield units

The mathematical technique allowing the reconstruction of

motion-free images from helically acquired CT data is called:

a. convolution

b. radon transformation

c. interpolation

d. Fourier reconstruction

interpolation

The full width at half maximum (FWHM) of a CT scanner is

used to describe:

a. spatial resolution

b. contrast resolution

c. noise

d. calibration accuracy

spatial resolution

A first-generation CT scanner consists of an x-ray tube and two

detectors that translate across the patient's head while rotating in

1-degree increments for a total of:

a. 45 degrees

b. 90 degrees

c. 180 degrees

d. 360 degrees

180 degrees

Which of the following abbreviations is used to identify a

computerized network that stores, retrieves, communicates, and

displays digital medical images?

a. WORM

b. PACS

c. DICOM

d. HIPAA

PACS

The CT “window” controls the __________ of the CT image as it appears to the viewer.

a. density and detail

b. spatial and contrast resolution

c. contrast and brightness

d. attenuation coefficient and Hounsfield value

contrast and brightness

Voxels with equal dimensions along the x-, y-, and z-axes are

referred to as:

a. prospective

b. isotropic

c. retrospective

d. anisotropic

isotropic

Which of the following artifacts is not affected by the CT

technologist?

a. motion

b. partial volume

c. edge gradient

d. ring

ring

When one is viewing a multiplanar reformation (MPR) image,

each pixel represents:

a. the maximum attenuation occurring within the voxel

b. the average attenuation occurring within the voxel

c. the minimum attenuation occurring within the voxel

d. all attenuation occurring within the voxel above a set threshold

value

the average attenuation occurring within the voxel

Statistical noise appears as __________ on a CT image.

a. decreased contrast

b. increased brightness

c. concentric circles

d. graininess

graininess

The component of the CT computer system responsible for the

data processing of image reconstruction is the:

a. pipeline memory

b. array processor

c. hard disk drive

d. RAM microprocessor

array processor

The loss of anatomic information between contiguous sections

due to inconsistent patient breathing is called:

a. cupping artifact

b. misregistration

c. overshoot artifact

d. out-of-field artifact

misregistration

Before a CT image can be reconstructed by a computer, the

transmission signal produced by the detectors must be converted

into numerical information by a(n):

a. kernel

b. analog-to-digital converter (ADC)

c. array processor

d. digital-to-analog converter (DAC)

analog-to-digital convertor (ADC)

A CT image is formed in part by projecting back all of the

attenuation values recorded during data acquisition onto a:

a. pixel

b. voxel

c. matrix

d. reformat

matrix

Areas of a CT image that contain abrupt changes in tissue

density are electronically represented by which of the following?

a. positive CT numbers

b. high spatial frequencies

c. negative CT numebrs

c. low spatial frequencies

high spatial frequencies

Which of the following components of CT image quality are

being evaluated in the figure?

1. low-contrast detectability

2. noise

3. uniformity

a. 2 only

b. 1 and 2 only

c. 1 and 3 only

d. 2 and 3 only

2 and 3 only

The differences in Hounsfield value exhibited in the regions of

interest (ROIs) measured on this CT image of a water-filled

phantom are most likely due to the phenomenon referred to as:

a. partial volume averaging

b. noise

c. beam hardening

d. detector drift

beam hardening

Which region of interest (ROI) on the figure demonstrates the

greatest amount of image noise?

a. 1

b. 2

c. 3

d. impossible to determine from the information provided

1

Which of the following terms is used to describe a set of rules

for solving a mathematical problem?

a. reconstruction

b. algorithm

c. function

d. array

algorithm

Which of the following factors does not affect the dimensions of

a voxel?

a. slice thickness

b. matrix size

c. kernel

d. display field of view

kernel

The size of the CT image displayed on a computer monitor can

be enlarged by increasing the:

1. display field of view (DFOV)

2. scan field of view (SFOV)

3. image magnification

a. 1 only

b. 3 only

c. 1 and 2 only

d. 1 and 3 only

3 only

The average photon energy of the primary beam of a CT

scanner operating at a tube potential of 120 kVp is

approximately:

a. 50 keV

b. 70 keV

c. 100 keV

d. 120 keV

70 keV

Multidetector CT (MDCT) systems typically employ which of

the following detector geometries?

a. first-generation

b. second-generation

c. third-generation

d. fourth-generation

third-generation

The acquisition of a series of CT images at a single anatomic

location over a set period is referred to as:

a. ultrafast CT

b. cine CT

c. conventional CT

d. temporal CT

cine CT

The rate at which a quantity of x-radiation emitted from a CT

tube passes through a unit area over a unit of time is called the:

a. effective mAs

b. photon flux

c. constant mAs

d. photon fluence

photon flux

An average CT number value for bone is:

a. +100 HU

b. +500 HU

c. +1000 HU

d. +3000 HU

+1000 HU

A standard CT image reconstructed on a 5122 matrix has a

digital size of approximately:

a. 0.5 MB

b. 3.0 MB

c. 5.0 MB

d. 10.0 MB

0.5 MB

The term used to describe the relationship between the linear

attenuation coefficient of an object and the calculated CT number

is:

a. linearity

b. mottle

c. quantum noise

d. spatial resolution

linearity

Quality control measurements to test the accuracy of the CT

scanner's calibration should be performed:

a. daily

b. weekly

c. monthly

d. annually

daily

The 3-D CT technique that includes all of the acquired voxel

information in the reconstructed model with adjustments to its

opacity is termed:

a. surface rendering

b. maximum intensity projection (MIP)

c. curved multiplanar reformation

d. volume rendering

volume rendering

Where is the high-frequency generator often located in a

modern CT scanner?

a. inside the gantry

b. just outside the scan room

c. beneath the CT table

d. inside the operator's console

inside the gantry

The smallest unit of information used in the binary language of

computers is the:

a. bit

b. chip

c. base

d. byte

byte

The continuous gantry rotation required by helical CT

acquisition is made possible by the application of:

a. electromagnetic bushings

b. titanium bearings

c. slip-rings

d. oil-cooled couplings

slip-rings

The process of applying a mathematical filter to remove

blurring from the reconstructed CT image is termed:

a. convolution

b. interpolation

c. iteration

d. z-filtration

convolution

Which of the following acquisitions may be characterized as

contiguous?

a. 2.5-mm sections reconstructed every 1.25 mm

b. 5.0-mm sections reconstructed every 7.5 mm

c. 3.75-mm sections reconstructed every 3.75 mm

d. 20-second cine acquisition with 1.25-mm sections

3.75-mm sections reconstructed every 3.75 mm

Pixels representing tissues with average attenuation coefficients

greater than that of water have which of the following types of

values?

a. extremely small

b. positive

c. negative

d. low contrast

positive

Digital CT images are networked and archived in accordance

with a standardized computer protocol identified by which of the

following abbreviations?

a. HIPAA

b. HTTP

c. TCP/IP

d. DICOM

DICOM

The contrast resolution of a CT scanner is not related to which

of the following?

a. focal spot size

b. section width

c. reconstruction algorithm

d. signal-to-noise ratio

focal spot size

The artifact present on the lateral borders of the image in the

figure most likely represents which of the following?

a. edge gradient

b. out-of-field artifact

c. tube arcing

d. beam hardening

out-of-field artifact

The image in the figure was produced using the following

parameters: large (full) scan field of view (SFOV); maximum

display field of view (DFOV) (48 cm); 200 mA, 120 kVp; soft

tissue algorithm. Which of the following technical adjustments

would serve to reduce the artifact present?

a. switching to a detail or bone algorithm

b. using a smaller SFOV

c. increasing the mA to 240 and the kVp to 140

d. centering the patient within the SFOV

centering the patient within the SFOV

The average photon energy of the CT x-ray beam can be

increased by:

a. increasing mAs

b. increasing filtration

c. increasing collimation

d. all of the above

increasing filtration

Which of the following is a solid-state device used to record the

light flashes given off by a scintillation crystal?

a. photomultiplier tube

b. anode

c. photodiode

d. input phosphor

photodiode

Automatic tube current modulation (ATCM) software is used

in current multidetector CT (MDCT) systems to control:

a. patient radiation dose

b. cardiac motion

c. timing of the contrast agent bolus

d. tissue perfusion assessment

patient radiation dose

The type of multidetector CT (MDCT) detector array that

contains multiple rows of detector elements, each of the same

length, is called a(n):

a. uniform matrix array

b. adaptive array

c. hybrid array

d. stationary array

uniform matrix array

A CT image is displayed in a window with a level of 0 and a

width of 500. Which of the following statements is correct?

a. Pixels with values between 0 HU and 500 HU will appear

white.

b. Pixels with values between −250 HU and +250 HU will be

assigned shades of gray.

c. Pixels with values greater than +500 HU will be black.

d. Pixels with values less than 0 HU will appear white.

Pixels with values between −250 HU and +250 HU will be

assigned shades of gray.

Reformatted CT image planes that lie perpendicular to the

original plane of acquisition may be described as:

a. oblique

b. orthogonal

c. obtuse

d. orthographic

orthogonal

Segmenting the data acquisition process into separate

components of smaller rotation angles may improve which of the

following components of CT image quality?

a. temporal resolution

b. longitudinal spatial resolution

c. contrast resolution

d. in-plane spatial resolution

temporal resolution

Which of the following image artifacts is unique to

multidetector CT (MDCT) systems?

a. step artifact

b. aliasing artifact

c. out-of-field artifact

d. cone beam artifact

cone beam artifact

Which of the following is considered an analytic form of image

reconstruction?

1. iterative technique

2. Fourier reconstruction

3. filtered back-projection

a. 1 only

b. 1 and 2 only

c. 2 and 3 only

2 and 3 only

A 16-slice MDCT system utilizes an adaptive array of 24

detectors, each ranging in size from 0.625 to 1.25 mm. What is the

maximum number of sections the system can acquire with each

rotation of the gantry?

a. 8

b. 16

c. 32

d. 64

16

The measurement of transmitted radiation made by an

individual detector is called a(n):

a. attenuation coefficient

b. Hounsfield value

c. CT number

d. ray sum

ray sum

The information included during the 3-D reconstruction of a

CT scan is controlled by the:

a. algorithm

b. window setting

c. threshold setting

d. grayscale map

threshold setting

The component of the CT scanner responsible for the

mathematical calculations of the image reconstruction process is

the:

a. data acquisition system (DAS)

b. analog-to-digital converter (ADC)

c. digital-to-analog converter (DAC)

d. array processor

array processor

Filament sizes for modern CT x-ray tubes range between:

a. 0.5 and 1.2 mm

b. 2.0 and 3.0 mm

c. 5.5 and 7.8 mm

d. 25.0 and 31.5 mm

0.5 and 1.2 mm

Which of the following would serve to increase spatial

resolution of a CT examinations using a large focal spot size, 5-

mm sections, and a 5122 matrix?

1. change to small focal spot size

2. acquire 2.5-mm sections

3. reconstruct images in a 3202 matrix

a. 1 only

b. 1 and 2 only

c. 1 and 3 only

d. 1, 2, and 3

1 and 2 onlt

A CT image is formed in part by projecting back all of the

attenuation values recorded during data acquisition onto a:

a. pixel

b. voxel

c. matrix

d. reformat

matrix

The mathematical process that allows multidetector CT

(MDCT) images to be reconstructed at any point along the

acquired volume is commonly referred to as:

a. iteration

b. filtered back-projection

c. Fourier reconstruction

d. z-filtering

z-filtering

Fourth-generation CT scanners use a __________ tube-detector

configuration.

a. rotate–translate

b. electron beam–stationary

c. rotate–stationary

d. rotate–rotate

rotate-stationary

Which of the following is considered an equipment-induced CT

image artifact?

a. step artifact

b. metallic artifact

c. cupping artifact

d. aliasing artifact

aliasing artifact

The measurement of CT system performance through quality

testing procedures and evaluation of the test results is referred to

as:

a. calibration

b. uniformity

c. quality assurance

d. linearity

quality assurance

During CT x-ray exposure, the product of the selected mA

setting and the scan time is called the:

a. effective mAs

b. peak mAs

c. absorbed mAs

d. constant mAs

constant mAs

Which of the following mathematical reconstruction methods

may be used by a CT system to decrease image noise and offer

patient dose savings?

a. convolution

b. iterative reconstruction

c. Fourier transform

d. back-projection

iterative reconstruction

What matrix size was used to reconstruct an image with a

display field of view (DFOV) of 25 cm and a pixel area 0.25 mm2?

a. 80 × 80 pixels

b. 256 × 256 pixels

c. 320 × 320 pixels

d. 512 × 512 pixels

512 × 512 pixels

When one is viewing a minimum intensity projection (min-IP)

image, each pixel represents:

a. the maximum attenuation occurring within the voxel

b. the average attenuation occurring within the voxel

c. the minimum attenuation occurring within the voxel

d. all attenuation occurring within the voxel above a set threshold

value

the minimum attenuation occurring within the voxel

Which of the following statements regarding predetector

collimation of the CT x-ray beam is true?

a. Predetector collimation reduces patient radiation dose.

b. Predetector collimation reduces the production of scatter radiation

c. Predetector collimation determines the scan field of view

(SFOV).

d. Predetector collimation removes scatter radiation before it

reaches the detectors.

Predetector collimation removes scatter radiation before it

reaches the detectors.

Which of the following would be considered the best method to

reduce respiratory motion on the CT image?

a. good patient–technologist communication

b. reduced scan times

c. immobilization devices

d. glucagon administration

good patient–technologist communication

Power output for a modern multidetector CT (MDCT) x-ray

tube has an approximate range of:

a. 3–5 kilowatts (kW)

b. 15–20 kilowatts (kW)

c. 40–48 kilowatts (kW)

d. 60–100 kilowatts (kW)

60–100 kilowatts (kW)

The mathematical manipulations required during the

reconstruction of a CT image are accomplished using a(n):

1. algorithm

2. kernel

3. mathematical filter function

a. 1 only

b. 1 and 2 only

c. 1 and 3 only

d. 1, 2, and 3

1, 2 and 3

When an operator reduces the scan field of view for a particular

body part, which of the following technical changes occurs?

1. The displayed image appears larger.

2. Spatial resolution increases.

3. A smaller number of detectors are activated.

4. The displayed image appears smaller.

A smaller number of detectors are activated.

An average CT number value for blood is:

a. −20 HU

b. +10 HU

c. +45 HU

d. +100 HU

+45 HU

The electronic combination of signals from adjacent detectors to

form a CT image is called:

a. binning

b. interpolation

c. z-filtering

d. partial volume averaging

binning

Which of the following technical adjustments may be employed

to improve the temporal resolution of a multidetector CT

(MDCT) system?

1. decrease in section width

2. image segmentation

3. physiologic gating

a. 1 only

b. 3 only

c. 1 and 2 only

d. 2 and 3 only

2 and 3

The streaking artifact that occurs in the area of the posterior

fossa during a CT examination of the brain may be referred to as:

a. cupping

b. the “boiled egg” artifact

c. stairstep

d. the Hounsfield bar

the Hounsfield bar

The relative accuracy between calculated CT numbers and their

respective linear attenuation coefficients is referred to as:

a. linearity

b. calibration

c. uniformity

d. contrast resolution

linearity

To maintain security and patient privacy when medical images

are transmitted across a network, the images may be coded in a

form decipherable only by software at the destination location.

This process is referred to as:

a. write-once, read-many (WORM)

b. Hypertext Transfer Protocol (HTTP)

c. teleradiology

d. encryption

encryption

Which of the following 3-D imaging techniques is utilized to

provide “fly-through” images during CT colonography?

a. orthographic volume rendering

b. shaded surface display (SSD)

c. perspective volume rendering

d. minimum intensity projection (min-IP)

perspective volume rendering

Which of the following sets of technical factors would yield an

isotropic data set when a multidetector CT (MDCT) image is

reconstructed using a 5122 matrix?

a. 5.0-mm sections, 17-cm DFOV

b. 3.0-mm sections, 25-cm DFOV

c. 1.25-mm sections, 48-cm DFOV

d. 0.625-mm sections, 32-cm DFOV

0.625-mm sections, 32-cm DFOV

Which of the following is not commonly used as a CT

scintillation detector material?

a. ceramic rare earth

b. silver halide

c. bismuth germanate

d. cadmium tungstate

silver halide

The mathematical technique that involves the estimation of an

unknown value from values on either side of it is known as:

a. filtering

b. interpolation

c. convolution

d. summation

interpolation

During which of the following CT examinations is a

misregistration artifact most likely to occur?

a. brain

b. pelvis

c. neck

d. abdomen

abdomen

In a single-slice CT (SSCT) system, which of the following

technical parameters may be adjusted retrospectively?

1. section width

2. section increment

3. reconstruction algorithm

a. 2 only

b. 1 and 2 only

c. 2 and 3 only

d. 1, 2, and 3

2 and 3 only

Bow-tie filters are employed in a CT x-ray system to reduce:

a. image noise

b. low spatial frequency signal

c. patient radiation dose

d. high spatial frequency signal

patient radiation dose

Which of the following technical factors is/are involved in the

determination of section width for multidetector CT (MDCT)images?

1. scan field of view (SFOV)

2. beam collimation

3. detector configuration

a. 2 only

b. 1 and 2 only

c. 1 and 3 only

d. 2 and 3 only

2 and 3 only

The fluctuation of CT numbers in an image of uniform,

homogeneous material may occur because of:

a. linearity

b. noise

c. aliasing

d. partial volume effect

noise

A region of interest (ROI) measurement placed over a portion

of a CT image provides which of the following?

a. distance (mm)

b. diameter (mm)

c. linear attenuation coefficient (μ)

d. average CT number (HU)

average CT number (HU)

Which of the following is the common term for the artifact

present on the image in the figure?

a. aliasing

b. streaking

c. edge gradient

d. tube arcing

streaking

Which of the following would be the most common cause of

the artifact in the figure?

a. metallic dental fillings

b. partial volume averaging

c. beam hardening

d. detector malfunction

metallic dental fillings

Reduction of the type of artifact seen in the figure on a coronal

multidetector CT (MDCT) view of the sinuses may be

accomplished through:

a. an increase in the mA

b. a decrease in the kVp

c. coronal multiplanar reformation (MPR) images built from an

axial acquisition

d. a reduction in the scan field of view (SFOV)

coronal multiplanar reformation (MPR) images built from an

axial acquisition

First-generation CT scanners used a method of data acquisition

based on a __________ principle.

a. multiplanar

b. rotation-only

c. translate–rotate

d. transaxial

translate–rotate

Compared with conventional radiography, computed

tomography produces diagnostic images with better:

a. low-contrast resolution

b. spatial resolution

c. minute detail

d. patient radiation dose reduction

low-contrast resolution

Writable CD and DVD media are optical disks that may be

described as:

a. read-only

b. lossy

c. write-once, read-many (WORM)

d. lossless

write-once, read-many (WORM)

Which of the following statements comparing the efficiency of

scintillation and gas ionization detectors is correct?

a. Both have approximately the same capture efficiency.

b. The scintillation detector has a higher capture efficiency.

c. Unlike the scintillation detector, the gas ionization detector has

a problem with afterglow.

d. Gas ionization detectors have a higher conversion efficiency.

The scintillation detector has a higher capture efficiency.

The data acquisition system (DAS) of a CT scanner is

responsible for:

1. measuring transmitted intensity

2. converting the transmission data into a digital signal

3. sending the digital information to the computer for processing

a. 1 only

b. 2 only

c. 1 and 3 only

d. 1, 2, and 3

1, 2 and 3

Which of the following is used to remove image blurring

during the back-projection method of CT image reconstruction?

1. z-filtering

2. convolution kernel

3. Feldkamp–Davis–Kress (FDK) algorithm

a. 2 only

b. 3 only

c. 1 and 2 only

d. 2 and 3 only

2 only

During CT x-ray production, the electromagnetic steering of

the electron beam from the cathode to two alternating targets is

referred to as:

a. prospective gating

b. ultrafast CT

c. twin CAT

d. flying focal spot

flying focal spot

The region of interest (ROI) measurement in the figure

provides an average density of +1.9 HU. This material is most

likely:

a. fat

b. blood

c. tumor

d. water

water

The image in the figure was most likely displayed with the use

of which of the following window widths?

a. 70

b. 400

c. 1300

d. 3800

400

Areas of a CT image that contain minimal changes in tissue

density are electronically represented by:

a. positive CT numbers

b. high spatial frequencies

c. negative CT numbers

d. low spatial frequencies

low spatial frequencies